U.S. Patent No. Re.24,906 discloses a pressure-sensitive adhesive tape, the adhesive of which consists essentially of a copolymer of 88 to 97 parts of alkyl acrylate and correspondingly 12 to 3 parts of a copolymerizable monomer such as acrylic acid. The copolymer provides excellent adhesion and holding power and experiences no substantial deterioration even after prolonged storage.
To improve certain properties, the acrylate copolymer adhesive has been crosslinked. For example, in U.S. Pat. No. 2,973,286, it is taught that solvent resistance is improved by crosslinking through the addition of an organic peroxide prior to the coating operation, and applying somewhat greater heat than would be necessary solely to dry the coating. U.S. Pat. Nos. 2,925,174; 4,286,047; 3,284,423; and 3,740,366 also are concerned with crosslinkable pressure-sensitive adhesive acrylate copolymers.
U.S. Pat. No. 4,396,675 discloses a crosslinkable adhesive comprising an acrylate copolymer of the type described in the aforemenlioned U.S. Pat. No. Re. 24,906, which consists of (a) a copolymer of greater than 90% of an acrylic acid ester of a non-tertiary alcohol, the only example of which is isooctyl acrylate, and less than about 10% of a copolymerizable monoethylenic monomer, such as acrylic acid, and (b) a latent crosslinking agent consisting of a lower alkoxylated amino formaldehyde condensate having C.sub.1-4 alkyl groups, the crosslinking agent being present in a concentration of from about 0.1 to 10% by weight of the copolymer.
U.S. Pat. No. 4,404,246 discloses another storage-stable crosslinkable pressure-sensitive adhesive again based on the acrylate copolymer as described in aforementioned U.S. Pat. No. Re. 24,906, wherein the copolymerizable monomer acid comprises from about 10 to about 25% by weight of the total monomer, the adhesive layer including a crosslinking agent of a lower-alkoxylated amino formaldehyde condensate having C.sub.1-4 alkyl groups in a concentration level of from about 0.1 to 0.8% by weiqht of the copolymer. This patent teaches the use of the acrylate monomer including both a C.sub.5-15 acrylate and a C.sub.1-4 acrylate, such as isooctyl acrylate and methyl, ethyl or butyl acrylates. The patent also teaches that levels of crosslinking agents above 0.8% should be avoided.
U.S. Pat. No. 4,329,384 discloses the use of polynuclear-chromophore-substituted halomethyl-s-triazines as crosslinkers for pressure-sensitive alkyl acrylate polymers.